Conventional photovoltaic (PV) inverters such as central or string inverters or inverters having a multiplicity of parallel strings carry out a number of additional functionalities in addition to their main task of converting the direct current produced by the PV generator to grid-compatible alternating current. Amongst others, these additional functionalities may be: communication with the user via an HMI (human-machine interface) or via other communication channels, grid monitoring functions, grid support functions, and safety functions.
Furthermore, the PV generator is kept at the maximum-power point by maximum-power point tracking (MPP tracking).
At the same time, the size of the PV generator is generally governed by the nominal power of the inverter, thus restricting the scalability of the overall photovoltaic system.
Since the current in a string is governed by the characteristics of its weakest PV module, only identical modules, or modules that are as similar as possible, of the same technology should be used within the string.
If the incident radiation on the PV generator is not homogeneous, for example because of partial shadowing, the maximum possible power cannot be extracted from the PV generator, because the PV modules have different optimum operating points (MPPs), which cannot be set individually in a series or parallel circuit.
The disadvantages of conventional PV inverters, like for example the restricted scalability, restrictions when modules of different types are used together and high sensitivity to incident radiation that is not homogeneous, are almost completely avoided when using inverters that are referred to as being close to the module, module-oriented or module-integrated (that is to say a dedicated inverter with an AC output and its own MPP tracking for each module, which is referred to in the following text as an AC module). However, if the intention is to integrate the additional functions mentioned at the beginning in an AC module, the specific price (costs related to the power) is considerably higher than for conventional PV inverters. Furthermore, the efficiency of the AC modules can, in principle, not reach the efficiency of conventional PV inverters. Until now, this has led to it not being possible to introduce AC modules to the market successfully.